Conventional gas cookers comprise a cooking field having several cooking zones, e.g. two, three or four cooking zones. Each cooking zone comprises a gas burner for heating a cooking recipient placed thereon, such as a cooking pot, a pan, etc. The gas burner comprises a gas inlet for supplying gas, a mixing device, e.g. in the form of a venturi pipe, for mixing the supplied gas with ambient air, and a plurality of outlet passages formed in a so-called flame crown for releasing the air/gas-mixture for subsequent combustion. Moreover, gas cookers are typically provided with a spark plug for igniting the air/gas-mixture leaving the flame crown, and with a supporting structure arranged above the burners for receiving cooking recipients thereon.
The gas burner of simple, conventional cooking zones is usually directly operated by means of a knob, which is provided at the operating panel of the gas cooker. The knob is operated to control a valve for adjusting the flow rate of the combustion gas, which is supplied to the gas burner via the gas inlet. Further developed cooking zones comprise an additional temperature sensor for sensing the actual temperature of the cooking recipient. The sensor probe of the sensor may be placed in a common plane with the upper side of the supporting structure, such that the sensor probe is in close contact with a cooking recipient placed thereon. Alternatively, the sensor probe can be held by a spring element in a position slightly above the plane defined by the upper side of the supporting structure. Accordingly—when a cooking recipient is placed on top of the support—the sensor probe is pushed down due to the self weight of the recipient and compresses the spring element. Thus a tight contact between the recipient and the sensor probe can be ensured. A cooking zone comprising such a temperature sensor is not controlled directly by the is above mentioned knob, but by a control device, which controls the flow rate of the combustion gas through the valve based on a comparison of a target temperature defined by the knob and the actual temperature detected by the temperature sensor. A cooking zone of this kind is known from GB 801,207.
The number and size of the outlet passages of the flame crown of a burner are adapted to the maximum gas flow rate for achieving the focussed maximum power of the burner. However, when the gas flow rate is reduced beyond a critical lower limit, the release of the air/gas-mixture cannot be maintained uniformly over all those outlet passages. Accordingly, this critical lower limit defines the minimum power, which can be realized by the burner. Normally, the ratio between the minimum power and the maximum power is 1 to 6. Due to the fact that the maximum and the minimum power of a burner depend from each other, it is hardly possible to provide a burner with a wide power range that enables an operation at very high as well as at very low power.
Starting from this prior art technology it is an object of the present invention to provide a gas burner of the above-mentioned kind, which can be operated within a wide power range. Moreover, it is an object of the present invention to provide a gas appliance comprising at least one of such gas burners and a method for operating such a gas burner.